Conventional integrated circuit (“IC”) device fabrication includes etching patterns of gaps into a metal layer such as aluminum. The gaps may then be filled with dielectric materials such as silicon dioxide. More recently, IC device fabricators are switching from aluminum to copper and other more conductive metals to take advantage of the lower resistance of these metals to electric current. In the case of copper, the metal's higher resistance to etching than aluminum is encouraging a switch to damascene processes where dielectric layers are deposited to form an integrated stack that are etched to create gaps for a subsequent metal gap-fill.
The dielectric layers that separate the layers of metal in a damascene structure are sometimes referred to as intermetal dielectric (IMD) layers. The capacitance (C) of the IMD material and the resistance (R) of the metal layers are significant components of the RC constant of the IC circuit. As the RC constant decreases, the circuit speed increases, and IMD layers having lower capacitance (i.e., lower dielectric constants “κ”) complement the lower resistance of metals like copper.
IMD layers typically include a barrier layer to prevent the diffusion of the metal into the adjacent dielectric layers. One material used for the barrier layer is silicon nitride (SixNy), which is also commonly used as an etch stop material for the formation of the damascene structures. Unfortunately, silicon nitride has a relatively high dielectric constant (κ=7.0 to 7.5 for Si3N4 compared to κ=4.0 to 4.2 for SiO2), which increases the overall κ value of the dielectric layer.
More recently, barrier layers have been developed from materials with lower dielectric constants. Silicon-carbon based barrier layers (e.g., silicon oxycarbide (SiOCH) barrier layers) have been developed that have lower dielectric constants than silicon nitride. One such layer, for example, is the BLOK™ (Barrier Low K) developed by Applied Materials, Inc. of Santa Clara, Calif. These low-κ barrier layers may be deposited by, for example, plasma enhanced chemical vapor deposition using trimethylsilane (TMS).
While silicon oxycarbide and other silicon-carbon based low-κ barrier layers have improved dielectric constants, they often have poor adherence to other low-κ silicon-carbon materials that make up the bulk dielectric portion of the IMD layer. Oxide films such as silicon dioxide (SiO2) adhere much better to the silicon-carbon based low-κ barrier layers, but also have higher κ values that raise the overall dielectric constant of the IMD layer. Thus, there is a need for methods of forming low-κ IMD layers that have good adhesion between the barrier layer and the bulk dielectric portion of the layer.